clear
clc

syms wc

% for first order stable butterworth filter the system function is
% defined on page p705
b=[wc];
a=[1 wc];

% for Wc=10*pi
Wc=10*pi;
b1=subs(b,wc,Wc);
a1=subs(a,wc,Wc);

w=linspace(0,1000);

H1=freqs(b1,a1,w);

% for single order butterworth filter, the zeros(z1), poles(p1) and scalar
% constant(k1) can be found as followsss
[z1,p1,k1]=butter(1,Wc,'s');

figure(1)
clf
plot(w,abs(H1));

return
